Recently, there is an accelerating demand to mount touch panels as the screen on mobile phones and other displays. While the touch panel has a screen kept bare, there are many chances of the finger or cheek coming in direct contact with the screen. Undesirably the touch panel is readily fouled with stains like sebum. There is an increasing need for technology to attain fingerprint proofness or easy stain removal on a display surface for better appearance or visibility. It is thus desired to have a material capable of meeting these requirements. In particular, for touch panel displays which are readily stained with fingerprints, it is desirable to form a water/oil repellent layer on their surface. Prior art water/oil repellent layers have high water/oil repellency and easy stain wipe-off, but suffer from the problem that the antifouling performance deteriorates during service. One of the factors accounting for deterioration of antifouling performance is a lack of weather resistance.
Generally, fluoropolyether-containing compounds exhibit, by virtue of their extremely low surface free energy, water/oil repellency, chemical resistance, lubricity, parting, antifouling and other properties. Taking advantage of these properties, they find use in a variety of industrial fields as water/oil repellent antifouling agents for paper and textiles, lubricants for magnetic recording media, oil-repellent agents for precision instruments, parting agents, cosmetic ingredients, protective films and the like. Inversely, the same properties indicate non-tackiness or non-adhesion to other substrates. Even if they can be coated to the substrate surface, it is difficult for the coating to tightly adhere thereto.
On the other hand, silane coupling agents are well known for their ability to bond surfaces of glass or fabric substrates to organic compounds. They are widely used as surface coating agents for numerous substrates. The silane coupling agent contains an organic functional group and a reactive silyl group (typically hydrolyzable silyl such as alkoxysilyl) in the molecule. In the presence of airborne moisture or the like, the hydrolyzable silyl groups undergo self-condensation reaction to form a coating. As the hydrolyzable silyl groups form chemical and physical bonds with the surface of glass or metal, the coating becomes a tough coating having durability.
Patent Documents 1 to 8 disclose a composition predominantly comprising a fluoropolyether-containing polymer-modified silane which is obtained by introducing a hydrolyzable silyl group into a fluoropolyether-containing compound, the composition being tightly adherent to the substrate surface and capable of forming a coating with water/oil repellency, chemical resistance, lubricity, parting, antifouling and other properties.
Lenses and antireflective coatings, when treated with the fluoropolyether-containing polymer-modified silane, are improved in lubricity, parting property and abrasion resistance, but lack weather resistance.
When substrates are surface treated with compositions comprising fluoropolyether-containing polymer-modified silanes, any of various coating techniques may be used to form a coating on the surface. In the subsequent step of curing the coating as applied via hydrolysis of hydrolyzable silyl groups, the hydrolysis reaction is typically accelerated at elevated temperatures of 80° C. to 120° C. or under humid conditions. Even at room temperature, hydrolyzable silyl groups slowly react with airborne moisture until a cured film is formed. Since the curing step requires hot humid conditions or the curing step at room temperature takes a time, the curing step can be a rate-determining or retarding factor for the manufacture process. Additionally, a coating (or water/oil repellent layer) which is cured under mild conditions, such as room temperature, in a short time has poor abrasion resistance and weatherability and its antifouling performance degrades during service.
Patent Document 9 discloses a coating composition to which fluorinated carboxylic acid is added as curing catalyst to accelerate cure so that a coating may be completed under mild conditions in a short time. However, abrasion resistance is adversely affected if the catalyst amount is reduced, and initial performance deteriorates if the catalyst amount is increased. There is a possibility that the carboxyl groups which are polar groups emerge on the outermost surface of the coating. If so, the coating does not perform well.
It is known to add a catalyst to accelerate hydrolysis reaction of alkoxysilyl groups. Prior art well-known catalysts include organotitanates such as tetrabutyl titanate and tetraisopropyl titanate; organotitanium chelate compounds such as titanium diisopropoxybis(ethyl acetoacetate) and titanium diisopropoxybis(methyl acetoacetate); organoaluminum compounds such as tris(acetylacetonato)aluminum and aluminum tris(ethyl acetoacetate); organozirconium compounds such as tetra(acetylacetonato)zirconium and zirconium tetrabutyrate; organotin compounds such as dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin di(2-ethyl hexanoate), dioctyltin dilaurate, dioctyltin diacetate, and dioctyltin dioctoate; metal salts of organic carboxylic acids such as tin naphthenate, tin oleate, tin butyrate, cobalt naphthenate, and zinc stearate; amine compounds and salts thereof such as hexylamine and dodecylamine phosphate; quaternary ammonium salts such as benzyl triethylammonium acetate; alkali metal salts of lower fatty acids such as potassium acetate; dialkylhydroxylamines such as dimethylhydroxylamine and diethylhydroxylamine; guanidyl-containing organosilicon compounds such as tetramethylguanidylpropyltrimethoxysilane; organic acids such as acetic acid and methanesulfonic acid; and inorganic acids such as hydrochloric acid and sulfuric acid. Regrettably, since these catalysts are not dissolved in fluorochemical solvents or even if soluble, only little dissolved, catalyst efficiency is low. In some cases, the metal value is left in the cured coating, adversely affecting the properties thereof.